This invention relates generally to motorized operators for circuit breakers used on electrical power systems and the like and specifically to electrical operators for such mechanically operated circuit breakers that may be readily installed on site, i.e. in the field.
One of the principal advantages of having the capability of electrically opening and closing circuit breakers is the ability to remotely operate the breaker in response to operator control as well as in response to fault currents. With electrically controlled motorized systems for opening and closing the circuit breakers, load switching and branch circuit protection may be rapidly and effectively accomplished because of the elimination of the need for a technician to physically manipulate the operating mechanism of the circuit breaker.
In many instances, it is desirable to upgrade a mechanically operated breaker by installing a motor control system therefor. Most of the motor control systems include mechanical electric switches to run the bidirectional motor in addition to limit switches for stopping the motor when the breaker reaches an operating position, i.e. either fully opened or fully closed. It is desirable to open or close a breaker rapidly and the limit switches, especially, are difficult and awkward to adjust in the field, and may be adjusted improperly.
As alluded to above, it is desirable that the circuit breaker operate to open or close all electrical phases as rapidly as possible and within a minimum time period for all phases. The motor drive must therefore rapidly start the motor, deliver very high torque for approximately 105 degrees of angular rotation, and rapidly stop. These severe requirements have necessitated the use of expensive apparatus that requires careful adjustment.
The present invention is directed to the combination of an electronically controlled bidirectionl high torque motor that operates a multiphase circuit breaker through a single reduction gear and a torque limited module. Transistor switches are used to drive the motor and limit switches are obviated by the use of a timed or predetermined duration of motor drive current and the torque limited module which includes a clutch. This permits the motor to overrun the breaker operation, i.e. the motor runs for a short time after the breaker has been fully operated, that is opened or closed. The electronic control system includes optical signal coupling devices for isolation purposes. The torque limited module and the electronic motor control system are individually the subjects of the above mentioned copending applications since they have separate utility apart from the present invention. The present invention is concerned with a field installable, nonadjustable, motor operator attachment for a circuit breaker.